New battery helps breaks barriers for low-cost energy storage

University of Southern California-led team develops a battery that could help California transition to renewable energy sources

A
team of researchers has developed a cheap, rechargeable and
eco-friendly battery that could be used to store energy at solar power
plants for a rainy day.

Led
by Sri Narayan, professor of chemistry at the USC Dornsife College of
Letters, Arts and Sciences, the team developed an air-breathing battery
that uses the chemical energy generated by the oxidation of iron plates
that are exposed to the oxygen in the air—a process similar to
rusting.

"Iron
is cheap and air is free," Narayan said. "It's the future." Details
about the battery will be published July 20 in the Journal of the
Electrochemical Society.

As
currently developed, Narayan's batteries have the capacity to store
between eight and 24 hours' worth of energy. His patent is pending, and
both the federal government and California utilities have expressed
interest in the project.

Iron-air
batteries have been around for decades—they saw a surge in interest
during the 1970s energy crisis, but suffered from a crippling problem: a
competing chemical reaction of hydrogen generation that takes place
inside the battery (known as hydrolysis) sucked away about 50 percent of
the battery's energy, making it too inefficient to be useful.

Narayan
and his team managed to reduce the energy loss down to 4%—making
iron-air batteries that are about 10 times more efficient than their
predecessors. The team did it by adding very small amount of bismuth
sulfide into the battery. Bismuth (which happens to be part of the
active ingredient in Pepto-Bismol and helps give the pink remedy its
name) shuts down the wasteful hydrogen generation.

Adding lead or mercury might also have worked to improve the battery's efficiency, but wouldn't have been as safe, Narayan said.

"A
very small amount of bismuth sulfide doesn't compromise on the promise
of an eco-friendly battery that we started with," he said.

The
California Renewable Energy Resources Act, signed into law by Gov.
Jerry Brown in April 2011, mandates that the state's utilities must
generate 33% of their power from renewable energy sources by the end of
2020.

This
aggressive push toward renewable energy sources presents utilities with
a problem: solar power works great on clear days and wind power is
wonderful on windy days, but what can they do when it's cloudy and calm
out? People still need electricity, and won't wait for the clouds to
clear to turn the lights on.

Currently,
solar and wind power make up a relatively small part of the energy used
in California. In 2009, 11.6% of electricity in the state was generated
by wind, solar, geothermal, biomass and small hydroelectric plants
combined. (Large hydroelectric plants accounted for an additional 9.2%.)
As such, dips in energy generation from solar and wind power plants can
be covered by the more predictable coal-burning grid.

As
California moves toward more renewable energy, solar- and wind-power
plants will need an effective way of storing large amounts of energy for
use during clouding and calm days.

Traditionally,
utilities store power by pumping water uphill into reservoirs, which
can then release the water downhill to spin electricity-generating
turbines as needed. This method is not always practical or even feasible
in drought-ridden California, where water resources are already in high
demand and open reservoirs can suffer significant losses due to
evaporation, Narayan said.

Batteries
have typically not been a viable solution for utilities. Regular sealed
batteries, like the AAs in your TV remote, are not rechargeable.
Lithium-ion batteries used in cell phones and laptops, which are
rechargeable, are at least 10 times as expensive as iron-air batteries.

Despite
his success, Narayan's work is still ongoing. His team is working to
make the battery store more energy with less material.

Funding
for this research came from the Advanced Research Projects Agency for
Energy (ARPA-E), an arm of the U. S. Department of Energy.